ABSTRACT An in vitro experiment was conducted during 2018–2020 at BARI, Bangladesh, Gazipur to screen the antagonistic effects of nine fungal and five bacterial antagonists against Sclerotinia sclerotiorum (Lib.) de Bary. White mold disease of mustard is one of the most important diseases of mustard caused by the phytopathogen S. sclerotiorum. Among the fungal antagonist tested, Aspergillus niger 2, A. niger 3, Penicilium sp, Trichoderma harzianum, T. viride and T. virens were most effective in inhibiting 89.35% to 100% mycelial growth of S. sclerotiorum in the dual culture method on PDA medium. Among these antagonist fungi, Aspergillus niger 2, A. niger 3, T. harzianum, T. viride and T. virens were capable of completely stopping the sclerotia formation of S. sclerotiorum. The Culture filtrates of Trichoderma species viz., T. harzianum, T. viride, T. virens completely (100%) inhibited the radial growth of the test pathogen. The highest inhibition of radial growth of S. sclerotiorum observed with the volatile metabolites of Trichoderma viride (90%) followed by T. harzianum (89.39%) and T. virens (89.35%). More than 90% of mycelial growth was inhibited by Pseudomonas sp. and Bacillus subtilis strain B20 in dual culture on PDA medium and also effective in stopping sclerotia formation. In the volatile method, all the tested antagonistic bacteria showed moderate antagonistic effects against S. sclerotiorum. Further study is required to develop effective formulation of those biocontrol agents for controlling this alarming pathogen in field condition in an eco-friendly manner. Keywords: White mould, Sclerotinia sclerotiorum, Antagonism, Biological control
ABSTRACT Streptomyces scabiei is a gram-positive soil dwelling actinobacteria, that causes the scab disease in many plants, especially in potatoes. This causes black blotches on the tuber that negatively impacts the economic and market worth of potatoes. Plant species like Chromolaena odorata and neem are known for their antibacterial potential against common human microflora and agricultural pathogens. Aiming to find natural solutions to plant pathogens, the current study analyzes, the antimicrobial effect of these plant extracts at different concentrations using well diffusion, MIC and MBC. Combination study was also performed to test the synergistic antimicrobial effect against Streptomyces scabiei. In addition, another soil dwelling bacteria, Paenibacillus polymyxa, known for its plant growth promoting potential was also tested against the plant pathogen to understand microbe-microbe interactions through cross streak assay. Both plant extracts showed promising antimicrobial effect against Streptomyces scabiei, however, they showed very less antimicrobial potential against the plant growth promoting bacterium. Moreover, cross streak assay showed that both the bacterium coexisted together. Hence, further studies can be conducted to formulate a biofertilizer containing the two-plant extract in optimum concentrations and Paenibacillus polymyxa to prevent scab disease and also enhance plant growth. Keywords: Well diffusion, MIC, MBC, Phytochemical analysis, FTIR analysis, GC-MS analysis.
ABSTRACT A total of 178 microbial cultures were isolated from rhizospheric soil, of which 45 cultures were identified as actinomycetes based on morphology. After primary and secondary screening, the actinomycete GK-121 was found to be a potent biocontrol agent for the rice blast pathogen Pyricularia oryzae. The culture was identified using conventional microscopy, Scanning Electron Microscope (SEM) and molecular characterization of the 16S rRNA sequence, and showed 99% similarity with Streptomyces maritimus, which was further confirmed by phylogenetic analysis. The culture exhibited a 45 mm zone of inhibition during in vitro screening against P. oryzae. The greenhouse experiment further proved the effectiveness of the isolate, as the seeds treated with S. maritimus showed very low disease incidence in plants inoculated with the pathogen P. oryzae, whereas untreated seeds showed high disease incidence. This is the first report to suggest that S. maritimus is effective in controlling the rice blast pathogen, P. oryzae, in vitro and in vivo. Keywords: Rhizosphere, Actinomycetes, Antiphytopathogenic activity, Molecular characterization, Biocontrol
Abstract This study assessed the dynamics of mosquito larval populations and species diversity in paddy fields in Alappuzha district, Kerala, and investigated the pesticide resistance of Culex tritaeniorhynchus and Culex sitiens to malathion and deltamethrin. Mosquito larvae were gathered biweekly over the three-month study duration. The density and diversity of research were evaluated independently for each category using the traditional diversity index. The World Health Organization (WHO) tube test was utilized to evaluate the pesticide susceptibility of adult Culex sitiens and Culex tritaeniorhynchus mosquitoes to malathion and deltamethrin. A total of 2,426 immature mosquitoes were captured. Two genera and ten species were gathered and identified as follows: Anopheles barbirostris, Anopheles peditaeniatus, Anopheles subpictus, Anopheles vagus, and five species of Culex: Cx. bitaeniorhynchus, Cx. gelidus, Cx. quinquefasciatus, Cx. sitiens, Cx. tritaeniorhynchus, and Cx. vishnui. Cx. tritaeniorhynchus exhibited intermediate tolerance to both malathion and deltamethrin, but Cx. sitiens shown great sensitivity to both pesticides under identical exposure settings. The increasing population of Culex tritaeniorhynchus mosquitoes in rice farming regions may present considerable threats to human health. An improved understanding of mosquito variety and pesticide resistance would facilitate the formulation of successful, regionally tailored vector control methods. Key words: Paddy field, Cx. tritaeniorhynchus, Cx. sitiens, pesticides, resistance
ABSTRACT An experimental investigation was carried out to evaluate the biocontrol efficacy of two Trichoderma species on pathogenic fungi isolated from the rhizospheric soil. Experiments revealed the beneficial interactions between the test biocontrol agents against the isolated pathogenic fungi. Two Trichoderma species viz. T. harzianum, and T. virens were assessed for their biological control efficiency against ten different pathogenic fungi viz. Alternaria alternata, Chaetomium cochliodes, Cladosporium cladosporoides, Colletotrichum fructicola, Curvularia lunata, Fusarium oxysporum, F. ventrichosum, F. proliferatum, F. solani and Mucor hiemalis. T. harzianum exhibited the highest mycelial growth inhibition against F. solani (71%), followed by C. cochliodes and C. lunata (70%), F. ventrichosum (69%), and C. fructicola (68%). Moderate inhibition was recorded against F. oxysporum, A. alternata, C. cladosporioides, and F. proliferatum (58–65%), while the lowest inhibition (44%) was observed against M. hiemalis. Similarly, T. virens showed maximum mycelial growth inhibition against C. fructicola (80%), followed by F. oxysporum (75%), C. cochliodes and C. lunata (72%), and F. proliferatum (70%). Inhibition against F. solani, A. alternata, F. ventrichosum and C. cladosporoides ranged from 59–68%, while the lowest inhibition was observed against M. hiemalis (54%). The study also assessed parameters such as the time to colony contact, overgrowth, and plate coverage by the biocontrol agent, pathogen radial growth, resistance, and Pakdaman’s Biological Control Index (PBCI). These attributes collectively also revealed the significant biocontrol efficacy of T. virens and T. harzianum against the tested soil-borne fungal pathogens. Keywords: Dual culture; confrontation; Trichoderma; growth inhibition; pathogen resistance
